Plasma membrane- boundary that separates the living cell from its nonliving surroundings
Selectively permeable- allowing some substances to cross it more easily than others
Made of a phospholipids bilayer
Phospholipids- amphipathic molecules- contains hydrophobic and hydrophilic regions
Textbook pg. 125
Davson and Danielli’s sandwich model stated the phospholipid bilayer lies between two layers of globular proteins (later studies found problems with this model)(Singer and Nicolson) Fluid Mosaic Model- a membrane is a fluid structure with a “mosaic” of various proteins embedded in it
Warm temperatures restrains movements of phospholipids
Cool temperatures maintains fluidity by preventing tight packing
Membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
Peripheral proteins- not embedded in membrane
Integral proteins- embedded in bilayer, penetrate the hydrophobic core and often span the membrane
Transmembrane proteins-integral proteins that span the membrane
6 major functions of membrane proteins:
Transport
Enzymatic activity
Signal transduction (cell communication)
Cell-cell recognition
Intracellular joining (gap/tight junctions)
Attachment to cytoskeleton and extracellular matrix (ECM)
cells recognize each other by binding to surface molecules on plasma membrance
carbohydrates may be covalently bonded to lipids forming glycolipids and bonding to proteins forming glycoproteins
Sidedness/Faces- a molecule that originates on the inside of the ER ends up on the outside face of the plasma membrane
Textbook pg. 129
Section 7.2
Nonpolar (hydrophobic) molecules- ex. hydrocarbons-dissolve in the lipid bilayer and can pass through the membrane rapidly
Polar molecules-ex. sugars-do NOT cross the membrane easily
Transport proteins-allows passage of hydrophilic substances across the membrane
Channel proteins- has a hydrophilic channel that certain molecules or ions can use as a tunnel
Aquaporins-channel proteins that facilitate the passage of water
- Carrier proteins- bind to molecules and change shape to shuttle them across the membrane
A is a channel protein and B is a carrier protein. Textbook pg. 134
7.3 diffusion- movement of molecules from an area of high concentration to an area of low concentration concentration gradient- the higher the concentration gradient, the steeper the difference. Materials move down from a high concentration to a low concentration gradient. passive transport- diffusion of a substance across a membrane with no added energy osmosis- diffusion of water through a selectively permeable membrane ALL OF THE ABOVE HAVE TO DEAL WITH THE NET MOVEMENT OF MOLECULES
isotonic- equal solute concentration-- no net movement of water (normal for animal cell) hypertonic- more solute concentration-- less water (causes a. cell to shrivel when placed in hypertonic solution) hypotonic- less solute concentration-- more water (causes a. cell to lyse/swell when placed in hypotonic solution) ALL OF THE ABOVE ARE COMPARISONS turgid- when a plant cell is placed in a hypotonic solution: desirable- allows plant to stay upright due to amount of pressure from the cell wall flaccid- when a plant cell is placed in an isotonic solution: there is not enough pressure for the plants to stay upright and so they wilt plasmolysis- when a plant cell is placed in a hypertonic solution: water leaves plant cell so the plant cell shrivels (plasma membrane separates from the cell wall)
facilitated diffusion- certain molecules aren’t chemically compatible with the membrane and have to have some sort of protein to help the molecules pass through the membrane. This is passive diffusion- you can have one of two proteins: a channel protein just provides a channel for the molecule to go through and can be gated or open or a carrier protein which changes shape due to the interaction between the protein and the transported molecule.
7.4 active transport- when a molecule wants to move against it’s concentration gradient, energy must be used to allow it to do so. Carrier proteins are used in active transport when they are phosphorylated by ATP. A classic example of this is the sodium-potassium pump:
Membrane potential is if there is a voltage across a membrane (if cells have an ion difference). This is measured in millivolts. The outside of the cell is positive in relationship to the inside-- both could be positive or negative but the outside is typically more positive and the inside typically more negative. Concentration and charge both drive the diffusion of ions across a membrane, the combination of these two is called the electrochemical gradient. Electrogenic pumps move ions. Examples of these are the proton pump and the sodium-potassium pump. When two proteins pair up they create a gradient that allows proteins to flow back in. This is called cotransport. For example: in plants, they use cotransport to put sucrose produced by photosynthesis into specialized cells in the veins of leaves. This is due to the proton pump: photo taken from: http://bioap.wikispaces.com/file/view/electrogenic.jpg/179935649/electrogenic.jpg
Section 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
small molecules and water enter or leave the cell through the lipid bilayer or by transport proteins
large molecules, such as polysaccharides and proteins, across the membrane via vesicles
Exocytosis:
Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cel. This is common when a cell produces substances for export.
In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents
Many secretory cells use exocytosis to export the products
Endocytosis:
Endocytosis describes the capture of a substance outside the cell when the plasma membrane merges to engulf it. The substance subsequently enters the cytoplasm enclosed in a vesicle.
In endocytosis, the cell takes in macromolecules only forming vesicles from the plasma membrane
Endocytosis is a reversal of exocytosis, in involving different proteins
There are three different kinds of endocytosis:
phagocytosis (“cellular eating”): cell engulfs the particle in a vacuole. It occurs when undissolved material enters the cell.
Pinocytosis (“cellular drinking”): cell creates a vesicle around fluid. It occurs when dissolved substances enter the cell.
Receptor-mediated endocytosis: Binding of ligands to receptors triggers vesicle formation. It occurs when specific molecules in the fluid surrounding the cell bind to specialized receptors that concentrate in coated pits in the plasma membrane.
ligands are molecules that bind to a receptor site of another.
Cholesterol travels in blood as low density lipoproteins (LDLs). Proteins transport the cholesterol in the blood and certain hormones target specific cells by receptor-mediate endocytosis.
Receptor mediated endocytosis removes LDLs to be used to make other steroids.
In humans with familial hypercholesterolemia, an inherited disease characterized by a very high level of cholesterol in the blood, the LDL receptor proteins are effective or missing, and the LDL particles cannot enter the cell.
See Ch. 7, part 2 ppt. slide 27
Section 48.1: Neuron Structure and Supporting Cells
Neuron Structure:
Most of a neuron’s organelles are in the cell body. The Cell Body contains the nucleus and other cellular organelles.
Most neurons have dendrites, highly branches extensions that receive signals from other neurons.
The axon is typically a long, slender extension of the cell body that sends nerve impulses or signals to other cells at synapse.
Many axons are covered with a myelin sheath.
Neurons have a wide variety of shapes that reflect their input and output interactions.
See Ch. 48 ppt. slide 2
Supporting cells are called Glia.
Glia are essential for structural wholeness of the nervous system.
The central nervous system (CNS) consists of the brain and spinal cord
Astrocytes provide structural support for neurons and regulate extracellular concentrations of ions and neurotransmitters
Oligodendrocytes (CNS) and Schwann cells (PNS - peripheral nervous system) form the myelin sheaths around axons of many vertebrate neurons
See Ch. 48 ppt. slide 4
48.2 Ion pumps and ion channels maintain the resting potential of a neuron · Membrane potential – electrical potential difference – exists across the plasma membrane of cells · Resting potential – the membrane potential of a neuron that is not transmitting signals - -70 mV · Sodium potassium pump · Gated ion channels – channels that open or close in response to stimuli o Voltage gated ion channels · Open and close when the membrane potential changes
48.3 Action potentials are the signals conducted by axons · Hyperpolarization – potassium ions flow out of the cell – the inside of the membrane becomes more negative · Depolarization – sodium ions flow into the cell and the inside of the cell becomes less negative – the inside of the membrane becomes less negative · The larger the stimulus, the larger the change is membrane potential · Threshold – the voltage needed to trigger the action potential · Action potential – it either happens or it doesn’t – the signals that carry information along axons · Sodium activation gates open in response to depolarization · Sodium inactivation gates close slowly in response to depolarization · Potassium channels open slowly in response to depolarization · Undershoot – the membrane is temporarily hyperpolarized because the potassium gates are open · Refractory period – the neuron can’t respond to another stimulus until it has recovered from the last stimulus – keeps the impulse going in one direction · Salutatory conduction – the action potential jumps along the axon from node to node – speeds up the conduction of the action potential · The region covered with the myelin sheath does not have a change in potential · The impulse goes in the gaps between the myelin sheath
48.4 Neurons communicate with other cells at synapses · Electrical synapse – the current flows directly from one cell to another through a gap junction · Most synapses are chemical synapses · A presynaptic neuron releases chemical neurotransmitters stored in the synaptic terminal · When an action potential reaches a terminal, the final result is a release of neurotransmitters into the synaptic cleft
Ions can pass through gap junctions to continue the flow => electrical synapse
The voltage change causes the calcium chamber to open and the calcium rushes in
The calcium goes to the edge and makes the vesicles dump their material (the neurotransmitter)
The neurotransmitter docks to the ligand gated ion channels and opens the gate
Ch. 7.1
Textbook pg. 125
- Davson and Danielli’s sandwich model stated the phospholipid bilayer lies between two layers of globular proteins (later studies found problems with this model)(Singer and Nicolson) Fluid Mosaic Model- a membrane is a fluid structure with a “mosaic” of various proteins embedded in it
- picture above- Textbook pg. 127- Freeze-fracture studies supported this
Textbook pg. 129
Section 7.2
- Nonpolar (hydrophobic) molecules- ex. hydrocarbons-dissolve in the lipid bilayer and can pass through the membrane rapidly
- Polar molecules-ex. sugars-do NOT cross the membrane easily
- Transport proteins-allows passage of hydrophilic substances across the membrane
- Channel proteins- has a hydrophilic channel that certain molecules or ions can use as a tunnel
- Aquaporins-channel proteins that facilitate the passage of water
- Carrier proteins- bind to molecules and change shape to shuttle them across the membraneA is a channel protein and B is a carrier protein.
Textbook pg. 134
7.3
diffusion- movement of molecules from an area of high concentration to an area of low concentration
concentration gradient- the higher the concentration gradient, the steeper the difference. Materials move down from a high concentration to a low concentration gradient.
passive transport- diffusion of a substance across a membrane with no added energy
osmosis- diffusion of water through a selectively permeable membrane
ALL OF THE ABOVE HAVE TO DEAL WITH THE NET MOVEMENT OF MOLECULES
isotonic- equal solute concentration-- no net movement of water (normal for animal cell)
hypertonic- more solute concentration-- less water (causes a. cell to shrivel when placed in hypertonic solution)
hypotonic- less solute concentration-- more water (causes a. cell to lyse/swell when placed in hypotonic solution)
ALL OF THE ABOVE ARE COMPARISONS
turgid- when a plant cell is placed in a hypotonic solution: desirable- allows plant to stay upright due to amount of pressure from the cell wall
flaccid- when a plant cell is placed in an isotonic solution: there is not enough pressure for the plants to stay upright and so they wilt
plasmolysis- when a plant cell is placed in a hypertonic solution: water leaves plant cell so the plant cell shrivels (plasma membrane separates from the cell wall)
facilitated diffusion- certain molecules aren’t chemically compatible with the membrane and have to have some sort of protein to help the molecules pass through the membrane. This is passive diffusion- you can have one of two proteins: a channel protein just provides a channel for the molecule to go through and can be gated or open or a carrier protein which changes shape due to the interaction between the protein and the transported molecule.
7.4
active transport- when a molecule wants to move against it’s concentration gradient, energy must be used to allow it to do so. Carrier proteins are used in active transport when they are phosphorylated by ATP.
A classic example of this is the sodium-potassium pump:
picture taken from: __http://bio1151.nicerweb.com/doc/class/bio1152/Locked/media/ch07/07_16SodiumPotassiumPump.jpg__
Membrane potential is if there is a voltage across a membrane (if cells have an ion difference). This is measured in millivolts. The outside of the cell is positive in relationship to the inside-- both could be positive or negative but the outside is typically more positive and the inside typically more negative.
Concentration and charge both drive the diffusion of ions across a membrane, the combination of these two is called the electrochemical gradient.
Electrogenic pumps move ions. Examples of these are the proton pump and the sodium-potassium pump.
When two proteins pair up they create a gradient that allows proteins to flow back in. This is called cotransport. For example: in plants, they use cotransport to put sucrose produced by photosynthesis into specialized cells in the veins of leaves. This is due to the proton pump: photo taken from: http://bioap.wikispaces.com/file/view/electrogenic.jpg/179935649/electrogenic.jpg
Section 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
Exocytosis:
Endocytosis:
Section 48.1: Neuron Structure and Supporting Cells
Neuron Structure:
- Most of a neuron’s organelles are in the cell body. The Cell Body contains the nucleus and other cellular organelles.
- Most neurons have dendrites, highly branches extensions that receive signals from other neurons.
- The axon is typically a long, slender extension of the cell body that sends nerve impulses or signals to other cells at synapse.
- Many axons are covered with a myelin sheath.
- Neurons have a wide variety of shapes that reflect their input and output interactions.
See Ch. 48 ppt. slide 2- Supporting cells are called Glia.
- Glia are essential for structural wholeness of the nervous system.
- They are also needed for functioning of neurons.
- There are four types of glia:
astrocytesradial glia
oligodendrocytes
Schwann cells
See Ch. 48 ppt. slide 4
48.2 Ion pumps and ion channels maintain the resting potential of a neuron
· Membrane potential – electrical potential difference – exists across the plasma membrane of cells
· Resting potential – the membrane potential of a neuron that is not transmitting signals - -70 mV
· Sodium potassium pump
· Gated ion channels – channels that open or close in response to stimuli
o Voltage gated ion channels
· Open and close when the membrane potential changes
48.3 Action potentials are the signals conducted by axons
· Hyperpolarization – potassium ions flow out of the cell – the inside of the membrane becomes more negative
· Depolarization – sodium ions flow into the cell and the inside of the cell becomes less negative – the inside of the membrane becomes less negative
· The larger the stimulus, the larger the change is membrane potential
· Threshold – the voltage needed to trigger the action potential
· Action potential – it either happens or it doesn’t – the signals that carry information along axons
· Sodium activation gates open in response to depolarization
· Sodium inactivation gates close slowly in response to depolarization
· Potassium channels open slowly in response to depolarization
· Undershoot – the membrane is temporarily hyperpolarized because the potassium gates are open
· Refractory period – the neuron can’t respond to another stimulus until it has recovered from the last stimulus – keeps the impulse going in one direction
· Salutatory conduction – the action potential jumps along the axon from node to node – speeds up the conduction of the action potential
· The region covered with the myelin sheath does not have a change in potential
· The impulse goes in the gaps between the myelin sheath
48.4 Neurons communicate with other cells at synapses
· Electrical synapse – the current flows directly from one cell to another through a gap junction
· Most synapses are chemical synapses
· A presynaptic neuron releases chemical neurotransmitters stored in the synaptic terminal
· When an action potential reaches a terminal, the final result is a release of neurotransmitters into the synaptic cleft